Much of the currently produced speech or musical sounds are recorded on magnetic tape. To produce a tape recording of speech or music, the sound is converted into corresponding electric signals by means of a microphone in conjunction with various amplification apparatus. These electric signals or voltage oscillations in turn produces variations in the strength of an existing magnetic field. The signals are thereby recorded on a magnetic tape which is magnetized along its length in accordance with the signals impressed on it.
In early tape recorders, steel wire or tape was used but has since been replaced by a plastic tape which is provided with a coating of powdered red iron oxide to provide a magnetic recording medium. The black oxide of iron is sometimes used for the same purpose. In any event, the oxide particles which are applied to the tape in a coating mixed with a binder substance, are strongly magnetizable and retain their magnetic properties almost indefinitely.
Sound is transmitted as pressure waves in the air. The lowest musical notes have a frequency of about 30 cycles per second. The highest notes of musical significance are about 4,000 cycles per second. The highest audible frequencies are in the 12,00 - 16,000 cycles per second range.
The tone color or timbre, however, consists of a complex mixture of frequencies, due to harmonies which may have as much as six times as high a frequency as that of the fundamental tone of the sound. All of these vibrations are picked up by the microphone, amplified and converted into variations in the magnetic field of an electromagnet in the recording head, whereby these variations are recorded on the magnetic tape.
To reproduce the sounds, the tape is passed over a similar head, called the reproducing head, at the same speed as that used in the recording. The magnetism stored in the tape induces voltage oscillations in the electromagnetic coil of the head and the electric signals thus produced are then used to energize a speaker.
The recording head consists of a coil wound about a core of magnetic iron which has a gap at the point where the tape moves across its surface. The current in the coil magnetizes the particles in the tape. During playback, the process is reversed. Thus, the recording head can be used as the reproducing head.
The faster the tape travels past the recording head, and subsequently past the reproducing head, the clearer will be the reproduction of the sound. This is for the reason that a higher tape speed provides more space for accommodating the highest frequencies on the tape. In order to record an overtone of, for example, 5,000 cycles per second, it is necessary to record 5,000 oscillations in the strength of the magnetic field on the tape during each second of its passage past the recording head. In ratio broadcasting, a tape speed of 15 inches per second is normally employed. Thus, each of the 5,000 oscillations has a space of 15/5,000 or 0.003 inches. Tape recorders for amateurs are usually operated at tape recording and playing speeds of 71/2 inches per second, 33/4 inches per second, or 17/8 inches per second. Most machines are provided, however, with means for providing any of these three speeds as is desired.
The widths of tape available for the recording of each oscillation of the overtone of 5,000 cycles per second are thus 0.0015 inches, 0.00075 inches, and 0.000375 inches, respectively. There is a progressive decline in recording and reproduction quality as the speed is lowered, since the width of the gap in the recording and reproduction head cannot be reduced indefinitely. Thus, each oscillation requires a certain minimum amount of space which is greater as the head and gap are of coarser construction. The greater the fineness and precision of the head, the more expensive is the tape recording equipment. To achieve high-fidelity recording and reproduction it is necessary to take many technical factors into account. Sound recorders for professional purposes generally include three motors, for example, one on the supply reel, one on the take-up reel, and a third motor drives the tape, Extreme care is taken to provide a smooth and uniform drive. Tape recorders for amateurs record generally on one-half of the 1/4 inch wide tape. Some machines are designed to record four or eight tracks on a 1/4 inch tape.
A great advantage of magnetic recording is that the recording can be erased and the tapes used over and over again. The erasure is done by the erasing head which produces a powerful and high alternating field that demagnetizes and thus erases the tape just before it passes the recording head.
This invention relates generally to eight-track tape cartridges and more particularly to a compact modular tape cartridge that fits inside a container, and can be used in an eight-track playing machine to perform the same functions of the larger eight-track tape cartridge. The eight-track tape cartridge assembly may be made of plastic by the injection molding procedure.
Eight-track tape cartridges contain a continuous loop of magnetic tape which is recorded in eight separate tracks. The tape travels through guides in the face of the cartridge with the recorded side of the tape facing the playback head in the eight-track playing machine. Depending on the type of playback head and depending on the number of tracks recorded on the tape to be read by the playback head, stereo, or quadraphonic sound may be played.
The music or message that is recorded on an eight-track tape continuously travels through the cartridge. The movement of the tape is due to the tape being pressed between a rotating pinch wheel built into the cartridge and the motorized capstan in the playing machine which moves the tape at a constant speed of 33/4 inches per second. The tape is spliced at the end of the recording with a conductive tape so that when the conductive tape passes in front of a switching device in the playing unit, the playing head physically moves to read a different set of tracks with a different song or message. The playback head may be designed to read two separate channels, or it may be designed to read four separately recorded tracks for quadraphonic sound, giving a total of two channels.
In the music industry, the average number of songs recorded on an eight-track stereo tape is three per channel. Though it is common knowledge in the music industry that one song per channel would provide the listener with immediate retrieval of a particular song, the cost of the conventional cartridge would still remain the same, and only a relatively small reduced cost of a shorter length of magnetic tape would be enjoyed.